Our investigations into the pathogenesis of the hypertension in the New Zealand strain of genetically hypertensive rats are concentrated in two areas. In the field of vascular reactivity the blood-perfused rat hind-limb preparation is being used (1) to study the interaction between humoral substances and neurally-released catecholamines, and (2) to determine whether altered reactivity in the hind limb precedes or is secondary to the hypertension. Renal haemodynamics in genetically hypertensive rats are being studied by means of a 133xenon washout technique to determine whether flow patterns differ in hypertensive and normotensive kidneys. BIBLIOGRAPHIC REFERENCES: Phelan, E.L., Simpson, F.O. and Smirk, F.H. Characteristics of the New Zealand strain of genetically hypertensive (GH) rats. Clin. exp. Pharmacol. Physiol. Suppl. 3, 5-10 (1976). Lee, D.R., Phelan, E.L. and Simpson, F.O. Effects of propranolol in genetically hypertensive rats. Proceedings of Second Symposium on the Spontaneously Hypertensive Rat, Newport Beach, California, 1976, in press.